Electrically conducting hydroprimer for plastics

ABSTRACT

An electrically conductive hydroprimer for plastics comprising I) at least one component comprising at least one aqueous polyurethane dispersion and at least one electrically conductive pigment; and II) at least one component comprising at least one polyisocyanate, wherein at least one of the components I and II comprise at least one aromatic solvent. Also, the use of the hydroprimer for producing multi-coat color and/or effect paint systems for plastic components and plastic components coated with the multi-coat paint systems.

This application is a National Phase Application of Patent ApplicationPCT/EP00/09754 filed on Oct. 05, 2000.

The present invention relates to a novel electrically conductivehydroprimer (water based primer) for plastics. The present inventionfurther relates to a novel process for painting plastics.

In industry nowadays the use is on the increase of plastic basedmoldings which are used together with metal parts and which require apaint finish. This is true particularly of automotive parts, which areincreasingly being manufactured from plastics parts, such as, forexample bumper fascias, spoilers, sills, wheel arch linings and sidetrims or protection strips.

In order to improve the impact strength, especially the low temperatureimpact strength, these plastics include hydrophobic oligomeric rubbers,which are fundamentally incompatible with aqueous paints. These rubberscontribute to the formation of a hydrophobic boundary layer betweenhydroprimer and plastics part and hence to the delamination of themulticoat paint system.

This problem can be countered by using organic solvent based primerswhich bring about a certain partial dissolution or partial swelling ofthe plastics surface and hence better anchoring of the primer coat.However, the high solvent content may lead to damage to the plasticspart as a result, for example, of microcracks. Moreover, in production,application, and curing, considerable quantities of solvents arereleased, which is no longer acceptable on environmental grounds.

It would be possible to prevent the delamination of hydroprimer coatingsby baking the hydroprimer film at temperatures >100° C. This cannot bedone, however, because of the absence of dimensional stability in themajority of plastics at these temperatures. Delamination of thehydroprimer coating can also be suppressed by flaming the surface of theplastics parts. This pretreatment, however, represents an additionalstep in the process and hence an additional cost factor and anadditional source of error.

It is an object of the present invention to find a novel hydroprimerplastics parts which no longer has the disadvantages of the prior artbut instead makes it possible to produce hydroprimer coatings formulticoat paint systems which adhere firmly, without delamination, evento unflamed plastics surfaces, and do so after thermal cure attemperatures <100° C. and which permit or assist the subsequentelectrostatic spray application of solid color topcoat materials,basecoat materials and/or clearcoat materials. Moreover, as part of amulticoat color and/or effect paint system, the primer coatings ought tohave excellent intercoat adhesion. Accordingly, the novel hydroprimerfor plastics has been found which comprises

I) at least one component comprising

A) at least one aqueous polyurethane dispersion

B) at least one electrically conductive pigment; and

II) at least one component comprising at least one polyisocyanate,

at least one of the components I and II comprising at least one aromaticsolvent (D).

Below, the novel electrically conductive hydroprimer for plastics isreferred to as “hydroprimer of the invention”.

Also found has been the novel process for producing multicoat colorand/or effect paint systems on plastics parts by

1a) applying the hydroprimer of the invention and heat curing theresultant hydroprimer film to give the electrically conductivehydroprimer coating; or alternatively

1b) applying the hydroprimer of the invention, drying the resultantelectrically conductive hydroprimer film, applying a light-coloredhydroprimer film, and jointly heat curing the resultant electricallyconductive hydroprimer film and the light-colored hydroprimer film, togive the electrically conductive hydroprimer coat and the light-coloredhydroprimer coat; and

2a) applying a solid-color topcoat material and heat curing theresultant solid-color topcoat film to give a solid-color topcoat; oralternatively

2b) applying an aqueous basecoat material and partially drying theresultant aqueous basecoat film, and

3) applying a clearcoat material and subjecting the resultant clearcoatfilm and the aqueous basecoat film to a joint heat cure or a heat cureand a cure with actinic light, to give the basecoat and the clearcoat.

Below, the novel process for producing multicoat color and/or effectpaint systems on plastics parts is referred to for the sake of brevityas “process of the invention”. In addition, the novel multicoat colorand or effect paint system for plastics parts has been found, whichcomprises the following coats atop one another in the stated sequence:

1a) a hydroprimer coating of the invention or alternatively

1a) a hydroprimer coating of the invention and

1b) a light-colored hydroprimer coating, and

2a) a solid-color topcoat or alternatively

2b) a basecoat, and

3) a clearcoat.

Below, the novel multicoat color and or effect paint system for plasticsparts is referred to as “multicoat paint system of the invention”.

Not least there have been found the novel plastics parts which arecoated with at least one multicoat paint system of the invention and/orwith at least one multicoat paint system produced by the process of theinvention and which are referred to below as plastics parts of theinvention. Further subject matter of the invention will emerge from thedescription which follows.

In the light of the prior art it was surprising and unforeseeable forthe skilled worker that the object of the present invention can beachieved specifically by adding comparatively small amounts of anaromatic solvent to the hydroprimer of the invention. In particular itwas surprising that this measure solved the problems of adhesion notonly between the plastics parts and the hydroprimer coating but alsobetween the hydroprimer coating and the other coatings present thereon,especially the light-colored hydroprimer coating, the solid-colortopcoat or the basecoat/clearcoat, and did so when a curing temperature≦100° C. was employed. In this context it proves to be a furthersurprising advantage of the hydroprimer of the invention that it doesnot cause any damage to the plastics parts as a result, for example, ofmicrocracking and of the emission of organic compounds during handlingand curing of the hydroprimer of the invention is not significantlyincreased as compared with conventional hydroprimers.

The hydroprimer of the invention is a two-component or multicomponentsystem, in particular a two-component system.

In the context of the present invention, this means a coating materialin which in particular the binder, especially the aqueous binderdispersion, and the crosslinking agent are present separately from oneanother in at least two components which are not combine d until shortlybefore application. This form is chosen when binder, especially theaqueous binder dispersion, and crosslinking agent react with one anothereven at temperatures ≦100° C., in particular at room temperature.Coating materials of this kind are employed in particular for coatingheat sensitive substrates such as plastic s parts.

The hydroprimer of the invention accordingly comprises at least one,especially one, component I and also at least one, especially one,component II, or consists of these components.

Component I includes as an essential constituent at least one,especially one polyurethane dispersion (A).

Suitable polyurethane dispersions (A) are customary and known and areavailable commercially. As is known, they comprise at least onewater-soluble or -dispersible polyurethane (A), which comprises, inparticular, polyester-polyurethanes (A).

Suitable polyester-polyurethanes (A) normally contain (potentially)cationic functional groups (a11) or (potentially) anionic functionalgroups (a12). Instead of these functional groups or in addition to themthey may contain nonionic functional groups (a13) based on polyalkyleneethers.

Examples of suitable functional groups (a11) for inventive use which canbe converted into cations by neutralizing agents and/or quaternizingagents are primary, secondary or tertiary amino groups, secondarysulfide groups or tertiary phosphine groups, especially tertiary aminogroups or secondary sulfide groups.

Examples of suitable cationic groups (a11) for inventive use areprimary, secondary, tertiary or quaternary ammonium groups, tertiarysulfonium groups or quaternary phosphonium groups, preferably quaternaryammonium groups or tertiary sulfonium groups, but especially quaternaryammonium groups.

Examples of suitable functional groups (a12) for inventive use which canbe converted into anions by neutralizing agents are carboxylic acid,sulfonic acid or phosphonic acid groups, especially carboxylic acidgroups.

Examples of anionic groups (a12) for inventive use are carboxylate,sulfonate or phosphonate groups, especially carboxylate groups.

Groups (a11) or (a12) should be selected in such a way that nodisruptive reactions, in particular no unwanted complexation and/or saltformation and/or crosslinking reaction, occur with the otherconstituents of component I or other constituents of the hydroprimer ofthe invention. The skilled worker is therefore able to make theselection in a simple manner on the basis of his or her art knowledge.

Examples of suitable neutralizing agents for functional groups (a11)which can be transformed into cations include inorganic and organicacids such as sulfuric acid, hydrochloric acid, phosphoric acid, formicacid, acetic acid, lactic acid, dimethylolpropionic acid or citric acid,especially formic acid, acetic acid or lactic acid.

Examples of suitable neutralizing agents for functional groups (a12)which can be transformed into anions include ammonia, ammonium salts,such as ammonium carbonate or ammonium hydrogen carbonate, for example,and also amines, such as trimethylamine, triethylamine, tributylamine,dimethylaniline, diethylaniline, tri-phenylamine, dimethylethanolamine,diethylethanolamine, methyldiethanolamine, triethanolamine, and thelike.

In general the amount of neutralizing agent is chosen so that from 1 to100 equivalents, preferably from 50 to 90 equivalents, of the functionalgroups (a11) or (a12) of the polyester-polyurethane (A) are neutralized.

The polyester-polyurethanes (A) are obtained by reacting

polyesterpolyols and

compounds which introduce the stabilizing (potentially) ionic groups(a11) or (a12) and/or the nonionic functional groups (a13), and ifdesired

polyamines and

amino alcohols

with polyisocyanates.

The polyesterpolyols are obtainable by reacting

unsulfonated or sulfonated saturated and/or unsaturated polycarboxylicacids or their esterifiable derivatives, together if desired withmonocarboxylic acids, and

saturated and/or unsaturated polyols, together if desired with monools.

Examples of suitable polycarboxylic acids are aromatic, aliphatic, andcycloaliphatic polycarboxylic acids. It is preferred to use aromaticand/or aliphatic, especially aromatic, polycarboxylic acids.

Examples of suitable aromatic polycarboxylic acids are phthalic acid,isophthalic acid, terephthalic acid, phthalic, isophthalic orterephthalic monosulfonate, or halophthalic acids, such astetrachlorophthalic or tetrabromophthalic acid, of which isophthalicacid is advantageous and is therefore used with preference.

Examples of suitable acyclic aliphatic or unsaturated polycarboxylicacids are oxalic acid, malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,undecanedicarboxylic acid, dodecanedicarboxylic acid or dimer fattyacids or maleic acid, fumaric acid or itaconic acid, of which adipicacid, glutaric acid, azelaic acid, sebacic acid, dimer fatty acids, andmaleic acid are advantageous and are therefore used with preference.

Examples of suitable cycloaliphatic and cyclic unsaturatedpolycarboxylic acids are 1,2-cyclobutanedicarboxylic acid,1,3-cyclobutanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid,1,3-cyclopentanedicarboxylic acid, hexahydrophthalic acid,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,4-methylhexahydrophthalic acid, tricyclodecanedicarboxylic acid,tetrahydrophthalic acid or 4-methyltetrahydrophthalic acid. Thesedicarboxylic acids can be used both in their cis form and in their transform, and also as a mixture of both forms.

Also suitable are the esterifiable derivatives of the abovementionedpolycarboxylic acids, such as, for example, their monoesters orpolyesters with aliphatic alcohols having from 1 to 4 carbon atoms orpolyols having from 1 to 4 carbon atoms. It is also possible,furthermore, to use the anhydrides of the abovementioned polycarboxylicacids, where they exist.

If desired it is possible together with the polycarboxylic acids to usemonocarboxylic acids as well, such as benzoic acid, tert-butylbenzoicacid, lauric acid, isononanoic acid, fatty acids of naturally occurringoils, acrylic acid, methacrylic acid, ethacrylic acid or crotonic acid,for example. A preferred monocarboxylic acid used is isononanoic acid.

Examples of suitable polyols are diols and triols, especially diols.Normally triols are used alongside the diols in minor amounts in orderto introduce branching into the polyesterpolyols.

Suitable diols are ethylene glycol, 1,2- or 1,3-propanediol, 1,2-, 1,3-or 1,4-butanediol, 1,2-, 1,3-, 1,4- or 1,5-pentanediol, 1,2-, 1,3-,1,4-, 1,5- or 1,6-hexanediol, neopentyl hydroxypivalate, neopentylglycol, diethylene glycol, 1,2-, 1,3- or 1,4-cyclohexanediol, 1,2-, 1,3-or 1,4-cyclohexanedimethanol, trimethylpentanediol,ethylbutylpropanediol, or the positionally isomeric diethyloctanediols.These diols may also be used per se for preparing the polyurethanes (A)for inventive use.

Further examples of suitable diols are diols of the formula I or II:

in which R¹ and R² each represent an identical or different radical andstand for an alkyl radical having from 1 to 18 carbon atoms, an arylradical or a cycloaliphatic radical, with the proviso that R¹ and/or R²must not be methyl;

in which R^(3, R) ⁴, R⁶, and R⁷ each represent identical or differentradicals and stand for an alkyl radical having from 1 to 6 carbon atoms,a cycloalkyl radical or an aryl radical and R⁵ represents an alkylradical having from 1 to 6 carbon atoms, an aryl radical or anunsaturated alkyl radical having from 1 to 6 carbon atoms, and n iseither 0 or 1.

Suitable diols I of the general formula I include all propanediols ofthe formula in which either R¹ or R² or R¹ and R² is not equal tomethyl, such as, for example, 2-butyl-2-ethylpropane-1,3-diol,2-butyl-2-methylpropane-1,3-diol, 2-phenyl-2-methylpropane-1,3-diol,2-propyl-2-ethylpropane-1,3-diol, 2-di-tert-butylpropane-1,3-diol,2-butyl-2-propylpropane-1,3-diol,1-dihydroxyrethylbicyclo(2.2.1-heptane, 2,2-diethylpropane-1,3-diol,2,2-dipropylpropane-1,3-diol or 2-cyclohexyl-2-methylpropane-1,3-diol,and others.

As diols II of the general formula II it is possible, for example, touse 2,5-dimethylhexane-2,5-diol, 2,5-diethylhexane-2,5-diol,2-ethyl-5-methylhexane-2,5-diol, 2,4-dimethylpentane-2,4-diol,2,3-dimethylbutane-2,3-diol, 1,4-(2′-hydroxypropyl)benzene and1,3-(2′-hydroxypropyl)benzene.

Of these diols, hexanediol and neopentyl glycol are particularlyadvantageous and are therefore used with particular preference.

The aforementioned diols may also be used per se for preparing thepolyester-polyurethanes.

Examples of suitable triols are trimethylolethane, trimethylolpropane orglycerol, especially trimethylolpropane.

The aforementioned triols may also be used per se for preparing thepolyester-polyurethanes (cf. patent EP-A-0 339 433).

If desired, minor amounts of monools may be used as well. Examples ofsuitable monools are alcohols or phenols such as ethanol, propanol,n-butanol, sec-butanol, tert-butanol, amyl alcohols, hexanols, fattyalcohols, allyl alcohol or phenol.

The polyesterpolyols may be prepared in the presence of small amounts ofa suitable solvent as azeotrope former. Examples of azeotrope formersused include aromatic hydrocarbons, such as in particular xylene and(cyclo)aliphatic hydrocarbons, e.g., cyclohexane or methylcyclohexane.

Further examples of suitable polyols are polyesterdiols obtained byreacting a lactone with a diol. They are notable for the presence ofterminal hydroxyl groups and repeating polyester fractions of theformula —(—CO—(CHR⁸)_(m)—CH₂—O—)—. In this formula the index m ispreferably from 4 to 6 and the substituent R⁸=hydrogen or an alkyl,cycloalkyl or alkoxy radical. No substituent contains more than 12carbon atoms. The total number of carbon atoms in the substituent doesnot exceed 12 per lactone ring. Examples thereof are hydroxycaproicacid, hydroxybutyric acid, hydroxy-decanoic acid and/or hydroxystearicacid.

Preferred for the preparation of the polyesterdiols is the unsubstitutedε-caprolactone, in which m has the value 4 and all R⁸ substituents arehydrogen. The reaction with lactone is started by low molecular masspolyols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol ordimethylolcyclohexane. It is, however, also possible to react otherreaction components, such as ethylenediamine, alkyldialkanol-amine orelse urea, with caprolactone. Further suitable diols of relatively highmolecular mass include polylactamdiols, which are prepared by reacting,for example, ε-caprolactam with low molecular mass diols.

Polyetherpolyols, in particular those having a number average molecularweight of from 400 to 5000, in particular from 400 to 3000, can be usedalongside the polyesterpolyols described above. Examples of highlysuitable polyetherdiols are those of the general formulaH—(—O—(CHR⁹)_(o)—)_(p)OH, where the substituent R⁹=hydrogen or a lower,optionally substituted, alkyl radical, the index o=2 to 6, preferably 3to 4, and the index p=2 to 100, preferably 5 to 50. Especially suitableexamples include linear or branched polyetherdiols such aspoly(oxyethylene) glycols, poly-(oxypropylene) glycols, andpoly(oxybutylene) glycols.

The polyetherdiols should on the one hand not introduce excessiveamounts of the ether groups, since otherwise the polyurethanes formedstart to swell in water. On the other hand, they can be used in amountswhich ensure the nonionic stabilization of the polyurethanes. In thatcase they serve as in-chain functional nonionic groups (a13).

(Potentially) cationic functional groups (a11) are introduced via theincorporation of compounds which contain in the molecule at least one,in particular two, groups which are reactive toward isocyanate groups,and at least one group which is capable of forming cations; the amountto be used can be calculated from the target amine number.

Suitable groups which are reactive toward isocyanate groups are, inparticular, hydroxyl groups and also primary and/or secondary aminogroups, of which the hydroxyl groups are used with preference.

Examples of suitable compounds of this kind are 2,2-dimethylolethyl- or-propylamine, which have been blocked with a ketone, the resultingketoxime group being hydrolyzed again before the cationic group (b11) isformed, or N,N-dimethyl-, N,N-diethyl- orN-methyl-N-ethyl-2,2-dimethylolethyl- or -propylamine.

(Potentially) anionic groups (a12) are introduced into the polyurethanemolecules by the incorporation of compounds which contain in themolecule at least one group which is reactive toward isocyanate groupsand one group which is capable of forming anions; the amount to be usedcan be calculated from the target acid number.

Examples of suitable compounds of this kind are those which contain inthe molecule two groups which are reactive toward isocyanate groups.Suitable groups which are reactive toward isocyanate groups are, inparticular, hydroxyl groups, and also primary and/or secondary aminogroups. Accordingly it is possible, for example, to use alkanoic acidshaving two substituents on the α-carbon atom. The substituent may be ahydroxyl group, an alkyl group or, preferably, an alkylol group. Thesealkanoic acids have at least one, generally from 1 to 3, carboxyl groupsin the molecule. They have from 2 to about 25, preferably from 3 to 10,carbon atoms. Examples of suitable alkanoic acids are dihydroxypropionicacid, dihydroxysuccinic acid, and dihydroxybenzoic acid. Oneparticularly preferred group of alkanoic acids are theα,α-dimethylolalkanoic acids of the general formula R¹⁰—C(CH₂OH)₂COOH,in which R¹⁰ stands for a hydrogen atom or an alkyl group having up toabout 20 carbon atoms. Examples of especially suitable alkanoic acidsare 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid,2,2-dimethylolbutyric acid, and 2,2-dimenthylolpentanoic acid. Thepreferred dihydroxyalkanoic acid is 2,2-dimethylolpropionic acid.Examples-of compounds containing amino groups are α,δ-diaminovalericacid, 3,4-diaminobenzoic acid, 2,4-diaminotoluenesulfonic acid, and2,4-diaminodiphenyl ether sulfonic acid.

Nonionic stabilizing poly(oxyalkylene) groups (a13) may be introduced aslateral or terminal groups into the polyurethane molecules. For thispurpose it is possible, for example, to use alkoxypoly(oxyalkylene)alcohols with the general formula R¹¹O—(—CH₂—CH¹²—O—)_(r)H in which R¹¹stands for an alkyl radical having from 1 to 6 carbon atoms, R¹² for ahydrogen atom or an alkyl radical having from 1 to 6 carbon atoms, andthe index r for a number between 20 and 75. (cf. patents EP-A-0 354 261or EP-A-0 424 705).

Suitable polyisocyanates include in principle all of the customary andknown polyisocyanates and polyisocyanate adducts that are used in thecoatings field and are aliphatic, cycloaliphatic,aliphatic-cycloaliphatic, aromatic, aliphatic-aromatic and/orcycloaliphatic-aromatic, these also being referred to as paintpolyisocyanates. Especially suitable polyisocyanates are diisocyanates.

Examples of suitable diisocyanates are isophorone diisocyanate(=5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane),5-isocyanato-1-(2-isocyanatoeth-1-yl)-1,3, 3-trimethylcyclohexane,5-isocyanato-1-(3-isocyanatoprop-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-(4-isocyanatobut-1-yl)-1,3,3-trimethyl-cyclohexane,1-isocyanato-2-(3-isocyanatoprop-1-yl)-cyclohexane,1-isocyanato-2-(3-isocyanatoeth-1-yl)cyclohexane,1-isocyanato-2-(4-isocyanatobut-1-yl)cyclohexane,1,2-diisocyanatocyclobutane, 1,3-diisocyanatocyclobutane,1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane,1,2-diiso-cyanatocyclohexane, 1,3-di isocyanatocyclohexane,1,4-diisocyanatocyclohexane, dicyclohexylmethane 2,41-diisocyanate,dicyclohexylmnethane 4,4′-diiso-cyanate, liquid dicyclohexylmethane4,4′-diisocyanate with a trans/trans content of up to 30% by weight,preferably 25% by weight, and in particular 20% by weight, which isobtainable by phosgenation of isomer mixtures ofbis(4-aminocyclohexyl)methane or by fractional crystallization ofcommercial bis(4-isocyanatocyclohexyl)methane in accordance with patentsDE-A-44 14 032, GB-A-1220717, DE-A-16 18 795 or DE-A-17 93 785,trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylenediisocyanate, hexamethylene diisocyanate, ethylethylene diisocyanate,trimethylhexane diisocyanate, heptamethylene diisocyanate ordiisocyanates derived from dimer fatty acids, such as are sold under thecommercial designation DDI 1410 by Henkel and described in patents WO97/49745 and WO 97/49747, especially2-heptyl-3,4-bis(9-isocyanato-nonyl)-1-pentylcyclohexane, 1,2-, 1,4- or1,3-bis(iso-cyanatomethyl)cyclohexane, 1,2-, 1,4- or1,3-bis(2-iso-cyanatoeth-1-yl)cyclohexane,1,3-bis(3-isocyanatoprop-1-yl)cyclohexane or 1,2-, 1,4- or1,3-bis(4-isocyanato-but-1-yl)cyclohexane, m-tetramethylxylylenediisocyanate (=1,3-bis(2-isocyanatoprop-2-yl)benzene or tolylenediisocyanate.

Alongside the diisocyanates it is possible to use polyisocyanates ofhigher functionality, having a statistical average functionality of from2.5 to 6, in particular from 2.5 to 5, in minor amounts. For thepurposes of the present invention, minor amounts are amounts which donot lead to gelling of the polyester-polyurethanes (A).

Examples of suitable polyisocyanates of higher functionality arepolyurethane prepolymers containing isocyanate groups, which can beprepared by reacting polyols with an excess of diisocyanates and arepreferably of low viscosity. It is also possible to use polyisocyanatescontaining isocyanurate, biuret, allophanate, iminooxadiazinedione,urethane, urea, carbodiimide and/or uretdione groups. Polyisocyanatescontaining urethane groups, for example, are obtained by reacting someof the isocyanate groups with polyols, such as trimethylolpropane andglycerol, for example. It is preferred to use the diisocyanatesdescribed in detail above.

Very particular preference is given to using mixtures of polyisocyanateadducts which contain uretdione and/or isocyanurate and/or allophanategroups and are based on hexamethylene diisocyanate, such as are formedby catalytic oligomerization of hexamethylene diisocyanate usingappropriate catalysts.

Gelling may also be prevented by using chain-terminating monoisocyanatesin addition. Examples of suitable monoisocyanates are hexyl isocyanate,nonyl isocyanate, lauryl isocyanate, stearyl isocyanate or phenylisocyanate.

The use of polyols, polyamines, and amino alcohols leads to an increasein the molecular weight of the polyurethanes (A).

Suitable polyols for the chain extension are polyols having up to 36carbon atoms per molecule such as ethylene glycol, diethylene glycol,triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane, castor oil orhydrogenated castor oil, di-trimethylolpropane ether, pentaerythritol,1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenolF, neopentyl glycol, neopentyl glycol hydroxypivalate, hydroxyethylatedor hydroxypropylated bisphenol A, hydrogenated bisphenol A or mixturesthereof (cf. patents EP-A-0 399 433, EP-A-0 436 941, EP-A-0 517 707).

Examples of suitable polyamines contain at least two primary and/orsecondary amino groups. Polyamines are essentially alkylene polyamineshaving from 1 to 40 carbon atoms, preferably from about 2 to 15 carbonatoms. They may carry substituents which have no hydrogen atoms that arereactive with isocyanate groups. Examples are polyamines having a linearor branched aliphatic, cycloaliphatic or aromatic structure andcontaining at least two primary amino groups.

Diamines include hydrazine, ethylenediamine, propylenediamine,1,4-butylenediamine, piperazine, 1,4-cyclohexyldimethylamine,1,6-hexamethylenediamine, tri-methylhexamethylenediamine,methanediamine, isophorone-diamine, 4,4′-diaminodicyclohexylmethane, andamino-ethylenothanolamine. Preferred diamines are hydrazine, alkyl- orcycloalkyldiamines such as propylenediamine and1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.

It is also possible to use polyamines containing more than two aminogroups in the molecule. In these cases, however, it should be ensured—byusing monoamines as well, for example—that crosslinked polyurethaneresins are not obtained. Polyamines of this kind which can be used arediethylenetriamine, triethylenetetramine, dipropylenediamine, anddibutylenetriamine. An example of a monoamine that may be mentioned isethylhexylamine (cf. patent EP-A-0 089 497).

Examples of suitable amino alcohols are ethanolamine, diethanolamine ortriethanolamine.

The polyurethanes may contain terminal and/or lateral olefinicunsaturated groups. Groups of this kind can be introduced, for example,with the aid of compounds which contain at least one isocyanate-reactivegroup, especially hydroxyl group, and at least one vinyl group. Examplesof suitable compounds of this kind are trimethylolpropane monoallylether or trimethylol-propane mono(meth)acrylate.

The polyurethanes (A) may be grafted with ethylenically unsaturatedcompounds. Examples of suitable polyurethanes (A) for use in accordancewith the invention which are present as graft copolymers are known frompatents EP-A-0 521 928, EP-A-0 522 420, EP-A-0 522 419 or EP-A-0 730613.

The preparation of the polyurethanes (A) has no special features interms of its method but instead takes place in accordance with thecustomary and known methods of polyurethane chemistry.

For preparing the hydroprimer of the invention the polyurethanes areneutralized with the neutralizing agents described above and dispersedin water to give a dispersion having a solids content of preferably from10 to 70%, more preferably from 20 to 60%, with particular preferencefrom 25 to 50%, and in particular from 30 to 45% by weight, based ineach case on the dispersion.

The further essential constituent of component I of the hydroprimer ofthe invention is at least one electrically conductive pigment (B).Examples of suitable electrically conductive pigments (B) are metalpigments, conductivity blacks, doped pearlescent pigments or conductivebarium sulfate. Especially suitable electrically conductive pigments arethe conductivity blacks. For further details, refer to Römpp LexikonLacke und Druckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998,“metal pigments”, p. 381 and “conductive pigments”, p. 354.

The amount of electrically conductive pigments (B) in the hydroprimer ofthe invention may vary very widely and is preferably from 0.01 to 10%,more preferably from 0.1 to 8%, with particular preferably from 0.5 to7%, with very particular preference from 0.5 to 6%, and in particularfrom 0.5 to 5% by weight, based in each case on the total amount of thehydroprimer of the invention.

The hydroprimer of the invention may comprise customary coatingsadditives (C) in effective amounts. Examples of suitable additives (C)are

organic and/or inorganic pigments, anticorrosion pigments and/or fillerssuch as calcium sulfate, barium sulfate, silicates such as talc,bentonite or kaolin, silicas, oxides such as aluminum hydroxide andmagnesium hydroxide, nanoparticles, organic fillers such as textilefibers, cellulose fibers, polyethylene fibers or wood flour, titaniumdioxide, carbon black, iron oxide, zinc phosphate or lead silicate;these additives may also be incorporated into the hydroprimers of theinvention by way of pigment pastes;

free radical scavengers;

organic corrosion inhibitors;

crosslinking catalysts such as organic and inorganic salts and complexesof tin, lead, antimony, bismuth, iron or manganese, preferably organicsalts and complexes of bismuth and of tin, especially bismuth lactate,ethylhexanoate or dimethylolpropionate, dibutyltin oxide or dibutyltindilaurate;

slip additives;

polymerization inhibitors;

defoamers;

emulsifiers, especially nonionic emulsifiers such as alkoxylatedalkanols and polyols, phenols and alkylphenols or anionic emulsifierssuch as alkali metal salts or ammonium salts of alkanecarboxylic acids,alkanesulfonic acids, and sulfo acids of alkoxylated alkanols andpolyols, phenols and alkylphenols;

wetting agents such as siloxanes, fluorous compounds, carboxylicmonoesters, phosphates, polyacrylic acids and their copolymers, orpolyurethanes;

adhesion promoters;

leveling agents;

film-forming auxiliaries such as cellulose derivatives;

flame retardants;

low molecular mass, oligomeric, and high molecular mass reactivediluents which may participate in thermal crosslinking, especiallypolyols such as tricyclodecanedimethanol, dendrimeric polyols,hyperbranched polyesters, polyols based on metathesis oligomers orbranched alkanes having more than eight carbon atoms in the molecule;

anticrater agents;

water-miscible organic solvents and/or

rheology control additives, such as those from patents WO 94/22968,EP-A-0 276 501, EP-A-0 249 201 or WO 97/12945; crosslinked polymericmicroparticles, such as those disclosed, for example, in EP-A-0 008 127;inorganic phyllosilicates, preferably smectites, especiallymontmorillonites and hectorites, such as aluminum magnesium silicates,sodium magnesium phyllosilicates and sodium magnesium fluorine lithiumphyllosilicates of the montmorillonite type or inorganic phyllosilicatessuch as aluminum magnesium silicates, sodium magnesium phyllosilicatesand sodium magnesium fluorine lithium phyllosilicates of themontmorillonite type (for further details, refer to the book by JohanBielemann “Lackadditive” [Additives for coatings], Wiley-VCH, Weinheim,New York, 1998, pages 17 to 30); silicas such as Aerosils; or syntheticpolymers containing ionic and/or associative groups such as polyvinylalcohol, poly(meth)acrylamide, poly(meth)acrylic acid,polyvinylpyrrolidone, styrene-maleic anhydride copolymers orethylene-maleic anhydride copolymers and their derivatives orhydrophobically modified polyacrylates; or polyurethane-basedassociative thickeners, as described in Römpp Lexikon Lacke undDruckfarben, Georg Thieme Verlag, Stuttgart, N.Y., 1998, “thickeners”,pages 599 to 600, and in the textbook “Lackadditive” by Johan Bieleman,Wiley-VCH, Weinheim, N.Y., 1998, pages 51 to 59 and 65;

Further examples of suitable coatings additives are described in thetextbook “Lackadditive” by Johan Bieleman, Wiley-VCH, Weinheim, NewYork, 1998.

Component II of the hydroprimer of the invention comprises or consistsof at least one polyisocyanate.

Examples of suitable polyisocyanates are those described above.

Preference is given to using the polyisocyanates having from 2.5 to 6,in particular from 2.5 to 5, isocyanate groups per molecule. Thesepolyisocyanates, advantageously, are liquid and advantageously haveviscosities of from 100 to 10,000, preferably from 100 to 5000, and inparticular—where manual mixing of components I and II is envisaged—from1000 to 2000 mPas (at 23° C.). If desired, small amounts of organicsolvent, preferably from 1 to 25% by weight based on straightpolyisocyanate, may be added to the polyisocyanates in order thereby toimprove the ease of incorporation of the isocyanate and, whereappropriate, to lower the viscosity of the polyisocyanate to a levelwithin the abovementioned ranges. Examples of suitable solvent additivesfor the polyisocyanates are ethoxyethyl propionate, amyl methyl ketoneor butyl acetate. Furthermore, the polyisocyanates may have beenhydrophilically or hydrophobically modified in a customary and knownmanner.

In the hydroprimer of the invention, the ratio of component I tocomponent II may vary very widely. It is guided in particular by theconcentration of the isocyanate-reactive groups in component I,particularly in the polyurethane (A), especially in thepolyester-polyurethane (A), and/or by the target crosslinking densityfor the hydroprimer coating of the invention. This ratio I:II isadvantageously from 100:1 to 100:20, preferably from 100:2 to 100:15,with particular preference from 100:3 to 100:13, with very particularpreference from 100:10 to 100:3.5, and in particular from 100:8 to100:4.

The inventively essential constituent of the hydroprimer of theinvention is at least one aromatic solvent (D). The aromatic solvent orsolvent mixture is present in component I or in component II. It mayalso be present, however, in both components I and II. Which variant isgiven preference in each case depends primarily on the component inwhich the aromatic solvent (D) can best be dissolved or dispersed. Theskilled worker is therefore able to determine the most favorable variantin each case on the basis of simple preliminary tests. In by far themajority of cases the addition of the aromatic solvent (D) to componentI proves particularly advantageous and is therefore employed withparticular preference.

Suitable aromatic solvents (D) include in principle all customary andknown liquid aromatic compounds which do not undergo any unwantedreactions with the other constituents of the hydroprimer of theinvention, especially the polyisocyanates, at the temperatures employedfor preparing, storing, applying, and heat curing the hydroprimers ofthe invention.

Suitable aromatic solvents (D) are selected from the group consisting ofmononuclear or polynuclear aromatics or heteroaromatics which areunsubstituted or are mono-, di- or trisubstituted by alkyl, cycloalkyl,perhaloalkyl, perhalocycloalkyl alkyloxy, cycloalkoxy and/orperhaloalkyloxy groups, it also being possible for said groups to belinked cyclically to the aromatic nucleus or nuclei, and alsomononuclear or polynuclear aromatics or heteroaromatics which are mono-,di- or trisubstituted by nitrile and/or nitro groups and/or halogenatoms.

Examples of suitable alkyl groups are methyl, ethyl, propyl, isopropyl,n-butyl, isobutyl and tert-butyl groups.

Examples of suitable cycloalkyl groups are cyclopentyl and cyclohexylgroups.

Examples of suitable perhaloalkyl groups are trifluoromethyl,pentafluoroethyl, and nonafluorobutyl groups.

Examples of suitable alkoxy groups are methoxy, ethoxy, propyloxy, andbutoxy groups.

Examples of suitable cycloalkoxy groups are cyclopentoxy and cyclohexoxygroups.

Examples of suitable perfluoroalkoxy groups are trifluoromethoxy,pentafluoroethoxy, and nonafluorobutoxy groups.

Examples of suitable cyclically linked groups are propane-1,3-diyl,butane-1,4-diyl, 1-oxabutane-1,4-diyl, 2-oxabutane-1,4-diyl, and1,4-dioxabutane-1,4-diyl groups.

Examples of suitable halogen atoms are fluorine, chlorine or bromine.

As aromatic solvents (D) it is preferred to use mononuclear aromaticsand/or heteroaromatics. With particular preference the aromatic nucleuscomprises a benzene nucleus and the heteroaromatic nucleus comprises athiophene, pyridine and/or triazine nucleus. Very particular preferenceis given to employing the benzene nucleus.

Examples of suitable aromatic solvents (D) based on the benzene nucleusare benzene, toluene, o-, m- and/or p-xylene, mesitylene, pseudocumene,hemellitene, ethylbenzene, cumene, p-cymene, tert-butylbenzene,chlorobenzene, o-, m- and/or p-dichlorobenzene, fluorobenzene, o-, m-and/or p-difluorobenzene, perfluorobenzene, nitrobenzene, benzonitrile,methoxybenzene, ethoxybenzene or thiophene, of which the xylenes areused with particular preference. Very particular preference is given tousing technical grade mixtures of the xylenes containing traces of otheralkylated aromatics. The strict xylene isomers, the isomer mixtures, andthe technical grade mixtures are referred to as “xylene” in the contextof the present invention.

The amount of aromatic solvents (D) in the hydroprimer of the inventionmay vary very widely. The general rule is not to use so much aromaticsolvent (D) that the plastics parts are incipiently dissolved to anundesirably high extent. Furthermore, there must be no demixing or phaseseparation in the hydroprimer of the invention and/or in component I.The only lower limit on the fraction of aromatic solvents (D) is imposedby the consideration that it is necessary to use sufficient solvents (D)that the effect according to the invention occurs. Preference is givento using from 0.1 to 10%, more preferably from 0.15 to 8%, withparticular preference from 0.2 to 6%, with very particular preferencefrom 0.25 to 4%, and in particular from 0.3 to 2% by weight, based ineach case on the hydroprimer of the invention, of aromatic solvents (D).

The preparation of the hydroprimer of the invention has no specialfeatures in terms of its method but instead takes place with the aid ofcustomary and known mixing techniques and apparatus such as dissolversand/or stirred mills.

The hydroprimer of the invention is used to produce the multicoat colorand/or effect paint systems of the invention, employing in particularthe process of the invention.

In accordance with the invention, the hydroprimer of the invention canbe used in particular by the process of the invention to coat allplastics and plastics parts such as are commonly employed nowadays.Examples of such plastics are ABS, AMMA, ASA, CA, CAB, EP, UF, CF, MF,MPF, PF, PAN, PA, PE, HDPE, LDPE, LLDPE, UHMWPE, PC, PET, PMMA, PP, PS,SB, PUR, PVC, RF, SAN, PBT, PPE, POM, PUR-RIM, SMC, BMC, PP-EPDM, and UP(abbreviations to DIN 7728T1) and polymer blends thereof, especiallyPPE/PA, PC/PBT or PC/ABS, and fiber-reinforced plastics based thereon.It is a particular advantage of the hydroprimer of the invention and ofthe process of the invention that for purposes of better adhesion of thehydroprimer the plastics parts need no longer be pretreated by flamingor by plasma treatment.

The process of the invention starts from the application of thehydroprimer of the invention to the surface of the plastics part to becoated and heat curing of the resultant hydroprimer film to give thehydroprimer of the invention. In this step of the process and thesubsequent step heat curing is preferably conducted at temperatureswhich pose no risk of deformation of the plastics parts. Preference isgiven to employing temperatures ≦100° C., in particular from 80 to 95°C.

Alternatively, in the first step of the process the hydroprimer of theinvention is applied, the resultant electrically conductive hydroprimerfilm is dried, a light-colored hydroprimer film is applied wet on wet,and the resultant electrically conductive hydroprimer film andlight-colored hydroprimer film are jointly heat cured to give thehydroprimer coating of the invention and the light-colored hydroprimercoating.

Examples of suitable light-colored hydroprimers for use in accordancewith the invention are likewise two-component systems. Their component Icomprises at least one hydroxyl-containing binder in solution ordispersion in water and at least one light-colored pigment, and theircomponent II comprises at least one polyisocyanate. Suitablehydroxyl-containing binders include polyesters, polyacrylates,polyurethanes, acrylated polyesters and/or acrylated polyurethanes,especially polyurethanes. Examples of suitable polyurethanes are theabove-described polyurethanes (A). Examples of suitable light-coloredpigments are the above-described pigments (B) and (C) and also thepigments described below, insofar as they are light in color and opaque.Suitable components II include the components II described above. Thisvariant of the process of the invention is employed when it is necessaryto color match between the dark hydroprimer coating of the invention andthe light-colored topcoat or basecoat.

In the second step of the process of the invention a solid-coloredtopcoat material is applied and the resultant solid-colored topcoat filmis heat cured to give a solid-colored topcoat.

As an alternative to this, in the second process step an aqueousbasecoat material is applied and the resultant aqueous basecoat film ispartially dried and in the third process step a clearcoat material isapplied (wet-on-wet technique) and the resultant clearcoat and theaqueous basecoat film are jointly heat cured or cured by means of heatand by means of actinic light (dual cure) to give the basecoat and theclearcoat.

In the context of the process of the invention, the clearcoat may alsobe further coated with an additional clearcoat material and theresultant clearcoat film may be cured thermally and/or with actinicradiation to give a highly mar resistant clearcoat (sealer).

Suitable aqueous basecoat materials comprise at least onehydroxyl-containing binder in solution or dispersion in water and atleast one color and/or effect pigment. They may additionally comprisethe above-described customary coatings additives (C) and also customarycrosslinking agents in the known, effective amounts.

Suitable solid-color topcoat materials likewise comprise at least onehydroxyl-containing binder and at least one color and/or effect pigment.They may also further comprise the above-described customary coatingsadditives (C) and also customary crosslinking agents in the known,effective amounts.

In the context of the process of the invention it is preferred to employaqueous basecoat materials.

Examples of suitable hydroxyl-containing binders are polyurethanesand/or acrylated polyurethanes, particularly the polyurethanes (A)described above.

The aqueous basecoat material may further comprise at least onehydroxyl-containing polyacrylate, hydroxyl-containing polyester and/orhydroxyl-containing acrylated polyester as additional binder(s)

Suitable color and/or effect pigments can be produced from organic orinorganic compounds. On the basis of this large number of suitablepigments, therefore, the aqueous basecoat material for inventive useensures a universal scope for use and allows the realization of a largenumber of color shades and optical effects.

Effect pigments which can be used include metal plate pigments such ascommercial aluminum bronzes, the chromated aluminum bronzes of DE-A-3636 183, commercial stainless steel bronzes, and nonmetallic effectpigments, such as pearlescent pigments and interference pigments, forexample. For further details refer to Römpp Lexikon Lacke undDruckfarben, Georg Thieme verlag, 1998, pages 176, “effect pigments” andpages 380 and 381 “metal oxide-mica pigments” to “metal pigments”.

Examples of suitable inorganic color pigments are titanium dioxide, ironoxides, Sicotrans yellow, and carbon black. Examples of suitable organiccolor pigments are thioindigo pigments indanthrene blue, Chromophthalred, Irgazine orange, and Heliogen green. For further details refer toRömpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, 1998, pages180 and 181, “iron blue pigments” to “black iron oxide”, pages 451 to453 “pigments” to “pigment volume concentration”, page 563 “thioindigopigments” and page 567 “titanium dioxide pigments”.

The fraction of the pigments in the aqueous basecoat material andsolid-colored topcoat may vary extremely widely and is guided primarilyby the opacity of the pigments, the desired shade, and the desiredoptical effect. In the aqueous basecoat material of the invention thepigments are present in an amount of preferably from 0.5 to 50%, morepreferably from 0.5 to 45%, with particular preference from 0.5 to 40%,with very particular preference from 0.5 to 35%, and in particular from0.5 to 30% by weight, based in each case on the total weight of theaqueous basecoat material. The pigment/binder ratio, i.e., the ratio ofthe pigments to the polyurethanes and any other binders that may bepresent, may also vary extremely widely. This ratio is preferably from6.0:1.0 to 1.0:50, more preferably from 5:1.0 to 1.0:50, with particularpreference from 4.5:1.0 to 1.0:40, with very particular preference from4:1.0 to 1.0:30, and in particular from 3.5:1.0 to 1.0:25.

These pigments may also be incorporated into the aqueous basecoatmaterials of the invention by way of pigment pastes, in which case thepolyurethanes (A), inter alia, are suitable grinding resins.

Suitable starting compounds for preparing the polyurethanes are thecompounds described above in connection with the preparation of thehydroprimers.

Examples of suitable crosslinking agents are amino resins, compounds orresins containing anhydride groups, compounds or resins containingepoxide groups, tris (alkoxycarbonylamino) triazines, compounds orresins containing carbonate groups, blocked and/or nonblockedpolyisocyanates, beta-hydroxyalkylamides, and compounds containing onaverage at least two groups capable of transesterification, examplesbeing products of the reaction between malonic diesters andpolyisocyanates or between esters and partial esters of polyhydricalcohols of malonic acid and monoisocyanates, as described by Europeanpatent EP-A-0 596 460.

Examples of highly suitable aqueous basecoat materials and also thecorresponding coatings are known from patents EP-A-0 089 497, EP-A-0 256540, EP-A-0 260 447, EP-A-0 297 576, WO 96/12747, EP-A-0 523 610, EP-A-0228 003, EP-A-0 397 806, EP-A-0 574 417, EP-A-0 531 510, EP-A-0 581 211,EP-A-0 708 788, EP-A-0 593 454, DE-A-43 28 092, EP-A-0 299 148, EP-A-0394 737, EP-A-0 590 484, EP-A-0 234 362, EP-A-0 234 361, EP-A-0 543 817,WO 95/14721, EP-A-0 521 928, EP-A-0 522 420, EP-A-0 522 419, EP-A-0 649865, EP-A-0 536 712, EP-A-0 596 460, EP-A-0 596 461, EP-A-0 584 818,EP-A-0 669 356, EP-A-0 634 431, EP-A-0 678 536, EP-A-0 354 261, EP-A-0424 705, WO 97/49745, WO 97/49747, EP-A-0 401 565, EP-B-0 730 613 or WO95/14721.

Particular advantages are afforded by physically curing aqueous basecoatmaterials, which are therefore employed with preference in accordancewith the invention.

Examples of suitable clearcoat materials are two-component clearcoatmaterials. As is known, the two component clearcoat materials comprise acomponent I having at least one hydroxyl-containing binder and acomponent II having at least one polyisocyanate. Until they are used inunison, components I and II are stored separately from one another.

Examples of suitable polyisocyanates are those described above.

Examples of suitable hydroxyl-containing binders are oligomeric orpolymeric, random, alternating and/or blocked, linear and/or branchedand/or comb, addition (co)polymers of ethylenically unsaturated monomersor polyaddition resins and/or polycondensation resins. For furtherdetails of these terms refer to Römpp Lexikon Lacke und Druckfarben,Georg Thieme Verlag, Stuttgart, New York, 1998, page 457, “polyaddition”and “polyaddition resins (polyadducts)” and also pages 463 and 464,“polycondensates”, “polycondensation”, and “polycondensation resins”.

Examples of highly suitable addition (co)polymers arepoly(meth)acrylates and partially hydrolyzed polyvinyl esters.

Examples of highly suitable polyaddition resins and/or polycondensationresins are polyesters, alkyds, polyurethanes, polylactones,polycarbonates, polyethers, epoxy resin-amine adducts, polyureas,polyamides or polyimides.

The hydroxyl-containing binders or resins for use in accordance with theinvention are oligomers and polymers. In the context of the presentinvention, oligomers are resins which contain at least 2 to 15 repeatingmonomer units in their molecule. In the context of the presentinvention, polymers are resins which contain at least 10 repeatingmonomer units in their molecule. For further details of these termsrefer to Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag,Stuttgart, New York, 1998, “oligomers”, page 425.

The hydroxyl-containing resins for use in accordance with the inventioncontain primary and/or secondary hydroxyl groups. It is a quitesubstantial advantage of the process of the invention that both kinds ofhydroxyl groups can be used. This makes it possible to tailor thereactivity of the resins by playing on steric effects.

The OH number of the hydroxyl-containing resins for use in accordancefor the invention may vary very widely and is preferably from 10 to 500,more preferably from 20 to 400, and in particular from 30 to 350 mgKOH/g.

The resin may further contain at least one functional group which onexposure to actinic radiation reacts with a group of its own kind orwith another functional group. These functional groups may already bepresent in the hydroxyl-containing resins for use in accordance with theinvention or may be introduced subsequently into the resins by means ofpolymer-analogous reactions.

Examples of suitable functional groups of this kind are allyl, vinylacrylate or methacrylate groups, especially acrylate groups. The actinicradiation may comprise electromagnetic radiation such as X-rays, UVradiation, visible light or near IR (NIR) light, or corpuscularradiation such as electron beams.

Of the hydroxyl-containing binders described above, thepoly(meth)acrylates, the polyesters, and the polyurethanes are used withpreference. Particular advantages result from the joint use of thepoly(meth)acrylates and of the polyesters.

Besides the binder and the polyisocyanates, the two-component clearcoatmaterials for use in accordance with the invention may further comprisethe above-described customary coatings additives in the known, effectiveamounts. It is self-evident that the only additives employed here willbe those which do not impair the transparency of the clearcoat. Furtherexamples of suitable additives for clearcoat materials are

crosslinking catalysts such as dibutyltin dilaurate, lithium decanoateor zinc octoate;

transparent fillers based on silicon dioxide, aluminum oxide, titaniumdioxide or zirconium oxide; for further details refer to Römpp LexikonLacke und Druckfarben, Georg Thieme Verlag, Stuttgart, 1998, pages 250to 252;

sag control agents such as ureas, modified ureas and/or silicas, asdescribed, for example, in the references EP-A-192 304, DE-A-23 59 923,DE-A-18 05 693, WO 94/22968, DE-C-27 51 761, WO 97/12945 or “farbe+lack”, 11/1992, pages 829 ff; and/or

flatting agents such as magnesium stearate.

Examples of suitable clearcoat materials for producing highly marresistant clearcoats are organically modified ceramic materials, whichare sold, inter alia, under the brand name ORMOCER®.

In the context of the process of the invention, the coating materialsdescribed above may be applied by any customary application method, suchas spraying, knife coating, spreading, flow coating, dipping,impregnating, trickling or rolling, for example. The plastics part to becoated may itself be at rest, with the application unit or equipmentbeing moved. Alternatively, the plastics part to be coated may be moved,with the application unit being at rest relative to the substrate orbeing moved appropriately. The choice of which method to employ isguided primarily by the size of the substrate. Accordingly, a largeplastics part will be coated first and foremost using movableapplication equipment.

Preference is given to using spray application methods, such ascompressed air spraying, airless spraying, high speed rotation,electrostatic spray application (ESTA), together if desired with hotspray application such as hot air spraying, for example. Application canbe conducted at temperatures of max. 70 to 80° C., so that suitableapplication viscosities are achieved without the coating material andits overspray, which may be intended for reprocessing, undergoing anychange or damage during the short period of thermal exposure.Accordingly, hot spraying can be configured in such a way that thecoating material is heated only very shortly in the spray nozzle or ashort way upstream of the spray nozzle.

The spray booth that is used for application may be operated, forexample, with an optionally temperature-controllable circulation systemwhich is operated with a suitable absorption medium for the overspray,an example being the coating material itself.

Where the clearcoat material includes constituents which arecrosslinkable with actinic radiation, application is carried out underillumination with visible light with a wavelength of more than 550 nm,or in the absence of light. This prevents material change or damage tothe coating material and the overspray.

In general, the electrically conductive hydroprimer film and thelight-colored hydroprimer film, the solid-colored topcoat film, thebasecoat film, and the clearcoat film are applied in a wet filmthickness such that curing thereof gives coats having the thicknesseswhich are necessary and advantageous for their functions. In the case ofthe hydroprimer coating of the invention this thickness is from 5 to100, preferably from 10 to 80, with particular preference from 10 to 60,and in particular from 10 to 40 μm; in the case of the light-coloredhydroprimer coat this thickness is from 5 to 100, preferably from 10 to80, with particular preference from 10 to 60, and in particular from 10to 40 μm; in the case of the topcoat it is from 5 to 90, preferably from10 to 80, with particular preference from 15 to 60, and in particularfrom 20 to 50 μm; in the case of the basecoat it is from 5 to 50,preferably from 10 to 40, with particular preference from 12 to 30, andin particular from 15 to 25 μm; and in the case of the clearcoat it isfrom 10 to 100, preferably from 15 to 80, with particular preferencefrom 20 to 70, and in particular from 25 to 60 μm.

Heat curing may take place after a certain rest period. This period mayhave a duration of from 30 s to 2 h, preferably from 1 min to 1 h, andin particular from 1 min to 45 min. The rest period serves, for example,for leveling and degassing of the paint films or for the evaporation ofvolatile constituents such as solvents. The rest period may be assistedand/or shortened by using elevated temperatures up to 90° C. and/or by areduced air humidity <10 g water/kg air, especially <5 g water/kg air,provided this does not entail any damage or change to the paint films,such as premature complete crosslinking.

Heat curing has no special features in terms of its method but insteadtakes place in accordance with the customary and known methods such asheating in a forced air oven or irradiation using IR lamps. Heat curingmay also take place in stages. Advantageously, heat curing is effectedat a temperature from 50 to 100° C., with particular preference from 80to 100° C., and in particular from 85 to 100° C., for a time of from 1min up to 2 h, with particular preference from 2 min up to 1 h, and inparticular from 3 min to 45 min.

Given an appropriate material composition of the coating material, heatcuring may be supplemented by curing with actinic radiation, for whichin particular UV radiation and/or electron beams may be used. Ifdesired, it may be supplemented or carried out with actinic radiationfrom other radiation sources. In the case of electron beams it ispreferred to operate under an inert gas atmosphere. This can be ensured,for example, by supplying carbon dioxide and/or nitrogen directly to thesurface of the paint film.

In the case of UV radiation curing as well it is possible to operateunder inert gas in order to prevent the formation of ozone.

Curing with actinic radiation is carried out using the customary andknown radiation sources and optical auxiliary measures. Examples ofsuitable radiation sources are high or low pressure mercury vapor lamps,which may have been doped with lead in order to open up a radiationwindow up to 405 nm, or electron beam sources. The arrangement of thesesources is known in principle and may be adapted to the circumstances ofthe work piece and the process parameters. In the case of work pieces ofcomplex shape, those regions not accessible to direct radiation (shadowregions) such as cavities, folds, and other structural undercuts may becured using pointwise, small-area or all-round emitters in conjunctionwith an automatic movement means for the irradiation of cavities oredges.

The equipment and conditions for these curing methods are described, forexample, in R. Holmes, “U.V. and E.B. Curing Formulations for PrintingInks”, Coatings and Paints, SITA Technology, Academic Press, London,United Kingdom 1984.

Curing may take place here in stages, i.e., by multiple exposure tolight or actinic radiation. It may also be done alternatingly, i.e., bycuring alternately with UV radiation and electron beams.

Where heat curing and actinic radiation curing are employed together(dual cure), these methods may be employed simultaneously oralternatingly. Where the two curing methods are used alternatingly, itis possible, for example, to begin with the heat cure and end with theactinic radiation cure. In other cases it may prove advantageous tocommence with the actinic radiation cure and end with it. The skilledworker is able to determine the method of curing that is particularlysuitable for each individual case, on the basis of his or her generalart knowledge with the assistance where appropriate of simplepreliminary tests.

The multicoat color and/or effect paint system of the invention,obtained in particular by the process of the invention, comprises thefollowing coats atop one another in the following sequence:

1a) a hydroprimer coating of the invention or alternatively

1a) a hydroprimer coating of the invention and

1b) a light-colored hydroprimer coating, and

2a) a solid-color topcoat or alternatively

2b) a basecoat, and

3) a clearcoat, and also, if desired,

4) a highly mar resistant clearcoat (sealer).

The multicoat color and/or effect paint systems of the invention exhibitan outstanding profile of properties which is very well balanced interms of mechanics, optics, corrosion resistance, and adhesion, even atvery low temperatures and/or following condensation exposure.Accordingly, the multicoat systems of the invention have the market'srequired high optical quality and intercoat adhesion, even in the steamjet test, and do not give rise to any problems such as deficientcondensation resistance, cracking (mud cracking), leveling defects orsurface textures.

In particular the multicoat paint system of the invention possesses anoutstanding metallic effect, an outstanding D.O.I. (distinctiveness ofthe reflected image), and an outstanding surface smoothness. It isstable to weathering, resistant to chemicals and bird droppings, marresistant, and exhibits very good reflow behavior.

A further key advantage is the very good overcoatability of themulticoat paint system of the invention, even without abrasion. As aresult it can be coated easily with customary and known highly marresistant coating materials based on organically modified ceramicmaterials.

Not least, however, it proves to be a very particular advantage that bymeans of the process of the invention it is possible to realize amulticoat paint system which is based predominantly on aqueous coatingmaterials.

Accordingly, the plastics parts of the invention also have a relativelylong service life, a better esthetic appearance, and improvedtechnological usefulness, so making them particularly attractiveeconomically.

EXAMPLE The Preparation of an Inventive Hydroprimer and its use forProducing an Inventive Multicoat Color and Effect Paint System

For producing the multicoat paint system of the invention, first of allcomponent I of the inventive hydroprimer was prepared as follows:

In a dissolver, 32 parts by weight of a commercialpolyester-polyurethane dispersion, 1.7 parts by weight of Aerosil, 1.3parts by weight of a commercial electrically conductive carbon black,6.0 parts by weight of a commercial 3% Bentone paste, 1.5 parts byweight of butyl glycol, 1.5 parts by weight of a 52% strength wettingagent solution, 23 parts by weight of titanium dioxide, 13 parts byweight of barium sulfate, 3.7 parts by weight of talc and 1.1 parts byweight of a commercial emulsifier were mixed with one another for 20minutes and up to a temperature of 60° C. Thereafter, the resultingmixture was ground in a stirred mill (ZWM mill) to a particle size offrom 12 to 14 μm (Hegman wedge 25). Subsequently, 10.2 parts by weightof water and one part by weight of xylene were added, to give thecomponent I for inventive use.

Shortly before application, component I was mixed with a commercialcycloaliphatic polyisocyanate (Desmodur® N 3400 from Bayer AG)(component II) in a weight ratio I:II of 100:6, after which theresulting inventive hydroprimer was applied by pneumatic sprayapplication in a dry film thickness of from 20 to 25 μm to plasticspanels made of Noryl® GTX 964 (commercial blend of polyphenylene oxideand polyamide). The resultant hydroprimer film was flashed off at roomtemperature for 10 minutes and cured at a panel temperature of 90° C.for 30 minutes.

The resultant inventive hydroprimer coating was then coated with acommercial aqueous basecoat material, after which the resultant aqueousbasecoat film was flashed off at room temperature for 10 minutes.Thereafter it was coated by the wet-on-wet technique with a commercialtwo-component clearcoat material, after which the aqueous basecoat filmand clearcoat film were cured jointly at a panel temperature of 90° C.for 30 minutes.

After the panels had been aged at 60° C. for 2 days, they were subjectedto the known DaimlerChrysler steam jet test. In the course of this testthere were no instances of delamination whatsoever, which underlines theoutstanding adhesion of the inventive hydroprimer to the plastics partson the one hand and to the aqueous basecoat on the other.

COMPARATIVE EXPERIMENT The Preparation of a Noninventive Hydroprimer andits use for Producing a Conventional Multicoat Color and Effect PaintSystem

The example was repeated except that no xylene was added to thehydroprimer. In the comparative experiment, in contrast to the example,severe delamination occurred during the DaimlerChrysler steam jet test.

What is claimed is:
 1. An electrically conductive hydroprimer forplastics comprising I) at least one component comprising A) at least oneaqueous polyurethane dispersion and B) at least one electronicallyconductive pigment; and II) at least one component comprising at leastone polyisocyanate, wherein at least one of the components I and IIcomprise at least one aromatic solvent that is at least one ofmononuclear aromatic, polynuclear aromatic, mononuclear heteroaromatic,and/or polynuclear heteroaromatic, wherein the aromatic solvent isunsubstituted or is mono-, di-, or tri-substituted by at least one of analkyl group, a cycloalkyl group, a perhaloalkyl group, aperhalocycloalkyl alkyloxy group, a cycloalkoxy group, a perhaloalkyloxygroup, a nitrile group, a nitro group and/or a halogen atom, andoptionally, wherein the alkyl group, the cycloalkyl group, theperhaloalkyl group, the perhalocycloalkyl alkyloxy group, thecycloalkoxy group, and/or the perhaloalkyloxy group can be linkedcyclically to the aromatic nucleus or nuclei wherein the mononucleararomatic is at least one of benzene, pseudocumene, hemellitene,ethyl-benzene, cumene, p-cymene, tert-butylbenzine, chlorobenzene,o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, flourobenzene,o-difluorobenzene, m-difluorobenzene, p-difluorobenzene,perfluorobenzene, nitrobenzene, benzonitrile, methoxybenzene, and/orethoxybenzene.
 2. The hydroprimer of claim 1, wherein the aromaticsolvent is present in the hydroprimer in an amount from 0.1 to 10% byweight based on the total weight of the hydroprimer.
 3. The hydroprimerof claim 1, wherein the aromatic solvent is selected from the groupconsisting of benzene, pseudocumene, hemellitene, ethyl-benzene, cumene,p-cymene, tert-butylbenzene, chlorobenzene, o-dichlorobenzene,m-dichlorobenzene, p-dichlorobenzene, fluorobenzene, o-difluorobenzene,m-difluorobenzene, p-difluorobenzene, perfluorobenzene, nitrobenzene,benzonitrile, methoxybenzene, ethoxybenzene, thiophene, and mixturesthereof.
 4. The hydroprimer of claim 1, wherein the polyurethanedispersion comprises at least one polyester-polyurethane containing atleast one of a cationic functional group; a functional group that can beconverted into a cation by at least one of a neutralizing agent and aquaternizing agent; an anionic functional group; a functional group thatcan be converted into an anion by a neutralizing agent; and/or anonionic functional group based on a polyalkylene ether.
 5. Thehydroprimer of claim 4, wherein the functional group that can beconverted into a cation is at least one of a primary amino group, asecondary amino group, a tertiary amino group, a secondary sulfidegroup, and/or a tertiary phosphine group; wherein the cationicfunctional group is at least one of a secondary ammonium group, atertiary ammonium group, a quaternary ammonium group, a tertiarysulfonium group, and/or a quaternary phosphonium group; wherein thefunctional group that can be converted into an anion is at least one ofa carboxylic acid group, a sulfonic acid group, and/or a phosphonic acidgroup; and wherein the anionic functional group is at least one of acarboxylate group, a sulfonate group, and/or a phosphonate group.
 6. Thehydroprimer of claim 1, wherein the polyester-polyurethane comprises areaction product of i) a polyesterpolyol ii) a compound that provides atleast one of a cationic functional group; a functional group that can beconverted into a cation by at least one of a neutralizing agent and aquaternizing agent; an anionic functional group; a functional group thatcan be converted into an anion by a neutralizing agent; and/or anonionic functional group based on a polyalkylene ether, and iii) apolyisocyanate, and optionally at least one of a polyamine and an aminoalcohol.
 7. The hydroprimer of claim 1, wherein the polyesterpolyolcomprises a reaction product of i) at least one of a polycarboxylic acidand/or an esterifiable derivative of a polycarboxylic acid, andoptionally further including a monocarboxylic acid, wherein i-a) thepolycarboxylic acid is unsulfonated or sulfonated i-b) thepolycarboxylic acid is saturated or unsaturated i-c) the esterifiablederivative of a polycarboxylic acid is unsulfonated or sulfonated, andi-d) the esterifiable derivative of a polycarboxylic acid is saturatedor unsaturated, and ii) at least one of a saturated polyol and/or anunsaturated polyol and optionally further including a monool.
 8. Thehydroprimer of claim 1, wherein the electrically conductive pigment isselected from the group consisting of a metal pigment, a conductivityblack pigment, a doped pearlescent pigment, a conductive barium sulfate,and mixtures thereof.
 9. The hydroprimer of claim 1, wherein thehydroprimer further comprises at least one of an electricallynonconductive pigment and/or a coatings additive.
 10. The hydroprimer ofclaim 1, wherein the hydroprimer has a solids content of from 30% to 80%by weight based on the weight of the hydroprimer.
 11. A processcomprising applying the hydroprimer of claim 1 to a substrate to producea multicoat paint system, wherein the paint system is one of a colorpaint system, an effect paint system, or a color and effect paintsystem.
 12. A process for producing a multicoat paint system on aplastic part, wherein the paint system is one of a color paint system,an effect paint system, and a color and effect paint system, comprisingI) applying the hydroprimer of claim 1 to the plastic part to provide ahydroprimer film, and one of Ia) heat curing the bydroprimer film togive an electrically conductive hydroprimer coating, or Ib) drying thehydroprimer film, applying a light-colored hydroprimer film, and jointlyheat curing the hydroprimer film and the light-colored hydroprimer filmto give an electrically conductive hydroprimer coat and a light-coloredhydroprimer coat; and II) one of IIa) applying a solid-color topcoatmaterial to form a film and heat curing the solid-color topcoat film togive a solid-color topcoat, or IIb) applying an aqueous basecoatmaterial to form a film and partially drying the aqueous basecoat film,applying a clearcoat material, and curing the resultant clearcoat filmand the aqueous basecoat film jointly to give a basecoat and aclearcoat, wherein the curing is one of i) heat curing or ii) heatcuring and a curing with actinic light.
 13. The process of claim 12further comprising coating the clearcoat with a further clearcoatmaterial to form a further clearcoat film and curing the furtherclearcoat film to give a mar resistant clearcoat, wherein the curing isone of i) heat curing or ii) heat curing and a curing with actiniclight.
 14. The process of claim 13, wherein the plastic part is one ofan automobile body or a commercial vehicle cab.
 15. The process of claim13, wherein at least one of: A. the aromatic solvent is present in thehydroprimer in an amount from 0.1 to 100% by weight based on the totalweight of the hydroprimer; B. the polyurethane dispersion comprises atleast one polyester-polyurethane containing at least one of a cationicfunctional group; a functional group that can be converted into a cationby at least one of a neutralizing agent and a quaternizing agent; ananionic functional group; a functional group that can be converted intoan anion by a neutralizing agent; and a nonionic functional group basedon a polyalkylene ether; C. the polyester-polyurethane comprises areaction product of i) a polyesterpolyol ii) a compound that provides atleast one of a cationic functional group; a functional group that can beconverted into a cation by at least one of a neutralizing agent and aquaternizing agent; an anionic functional group; a functional group thatcan be converted into an anion by a neutralizing agent; and a nonionicfunctional group based on a polyalkylene ether, and iii) apolyisocyanate, and optionally at least one of a polyamine and an aminoalcohol; D. the polyesterpolyol comprises a reaction product of i) atleast one of a polycarboxylic acid and an esterifiable derivative of apolycarboxylic acid, and optionally further including a monocarboxylicacid, wherein i-a) the polycarboxylic acid is unsulfonated or sulfonatedi-b) the polycarboxylic acid is saturated or unsaturated, i-c) theesterifiable derivative of a polycarboxylic acid is unsulfonated orsulfonated, and i-d) the esterifiable derivative of a polycarboxylicacid is saturated or unsaturated, and ii) at least one of a saturatedpolyol and an unsaturated polyol and optionally further including amonool; E. the electrically conductive pigment is selected from thegroup consisting of a metal pigment, a conductivity black pigment, adoped pearlescent pigment, a conductive barium sulfate, and mixturethereof; F. the hydroprimer further comprises at least one of anelectrically nonconductive pigment and a coatings additive; and/or G.the hydroprimer has a solids content of from 30% to 80% by weight basedon the weight of the hydroprimer.